A Green and Scalable Synthesis of Na₃ Fe₂ (PO₄ )P₂ O₇ /rGO Cathode for High-Rate and Long-Life Sodium-Ion Batteries

Sodium-ion battery has been considered as one of the most promising power sources for large-scale energy storage systems due to its similar electrochemistry to the lithium-ion battery and the crust abundance of Na resources. Essentially, developing low-cost electrode materials along with a facile and economical synthesis procedure is critically important to promote the commercialization of sodium-ion batteries. However, applicable cathode materials capable of being massively produced are still scarcely reported to date. Herein, a green and scalable synthesis approach is developed to obtain Na₃ Fe₂ (PO₄ )P₂ O₇ (NFPP)/rGO composite by using FePO₄ and Na₃ PO₄ as the resources, during which all the atoms present in the starting materials end up in the product. The prepared Na₃ Fe₂ (PO₄ )P₂ O₇ /rGO cathode exhibits an ultralong cycle life (capacity retention of 72.4% after 8000 cycles at 20 C) and outstanding rate capability (42.4 mAh g^-1 at 100 C). In particular, the NFPP/rGO-HC full battery assembled by the Na₃ Fe₂ (PO₄ )P₂ O₇ /rGO cathode and hard carbon anode demonstrates an energy density of 192 Wh kg^-1 and superior cycling performance (capacity retention of 85.2% after 500 cycles). These results will contribute to the development of sodium-ion batteries from applicable Na₃ Fe₂ (PO₄ )P₂ O₇ /rGO cathode material.